Soft ionization GC-HRMS of n-Alkanes C8 - C20 (SCIEX TripleTOF® 5600)

Importance of the Topic

Mineral oil saturated hydrocarbons (MOSH), composed predominantly of n-alkanes, pose analytical challenges due to their structural similarity and lack of ionizable functional groups. Soft ionization techniques are crucial for preserving molecular ions and improving the identification and quantification of these compounds in environmental and food matrices.

Objectives and Study Overview

This work presents a novel hyphenation of gas chromatography with Soft Ionization by Chemical Reaction In Transfer (SICRIT®) coupled to high-resolution mass spectrometry (GC-SICRIT®-HRMS) for the trace analysis of nonpolar n-alkanes C8–C20. The goal is to combine efficient chromatographic separation with gentle ionization to overcome limitations of traditional GC-EI-MS in MOSH analysis.

Methodology and Instrumentation

• Sample: Standard mixture of n-alkanes (C8–C20) at 40 mg/L in hexane
• Gas chromatograph: Agilent 7890 with split injection (1 μL, split ratio 1:10)
• Column: Restek Rxi-5ms, 30 m × 0.25 mm ID, 0.25 μm film
• Carrier gas: Helium at constant flow 2 mL/min
• Oven program: 40 °C (2 min), ramp 20 °C/min to 280 °C (6 min hold)
• Ion source: SICRIT® cold-plasma soft ionization (1.5 kV, 15 kHz)
• Mass spectrometer: SCIEX TripleTOF 5600 HRMS

Main Results and Discussion

• Complete separation of all 13 n-alkane standards (C8–C20)
• Dominant formation of [M+O−3H]+ and [M+2O−H]+ species with minimal fragmentation
• High-resolution mass measurements with mass errors within a few ppm
• Enhanced isomer confirmation based on exact mass of adduct ions
• Preliminary detection limits estimated in the low ppb range

Benefits and Practical Applications

• Soft ionization preserves molecular information for unambiguous identification
• High sensitivity and selectivity for nonpolar saturated hydrocarbons
• Potential for standardized MOSH quantification in environmental and food analysis
• Seamless integration with existing GC-MS platforms

Future Trends and Possibilities

• Extension to additional nonpolar analyte classes
• Automation of data processing for complex hydrocarbon profiles
• Integration into quality control workflows across industries
• Hybrid coupling with other separation techniques for improved throughput

Conclusion

The GC-SICRIT®-HRMS approach offers a powerful, easy-to-implement solution for the soft ionization and high-resolution detection of n-alkanes, addressing key limitations of traditional GC-MS methods and advancing the analysis of MOSH in various matrices.

Reference

1. Alam MS, Stark C, Harrison RM. Anal. Chem. 2016;88(8):4211–4220.
2. Mirabelli MF, Wolf J-C, Zenobi R. Analyst. 2017;142:1909–1915.
3. Nunome Y, Kodama K, Ueki Y, et al. Talanta. 2019;204:310–319.